Wind energy is one of the more extended renewable energy resources. This kind of energy easily covers a wide power range with reduced costs.
Nowadays, the most common application of wind energy is the utility-scale generation by means of wind farms consisting on several large turbines, each one with a power of at least 800 kW. However, a newer and promising application is the use of small and medium size turbines (normally below 500 kW) in distributed generation.
The size of these turbines allows placing them near to the point where the generated energy will be used. In those cases it is not necessary a transport grid. The use of small and medium size turbines makes it possible to generate renewable energy at low cost close to factories or industrial areas, for example.
For the reasons above, the development of small and medium size wind turbines is increasing nowadays.
One difficulty in small and medium turbines is that their relatively small size makes it impossible to apply the usual solutions of large wind turbines to allow the maintenance personnel both accessing and working on the components of the nacelle.
Indeed, the nacelle of large turbines is reached by means of a ladder or, more commonly, an elevator inside the tower, and once there the maintenance operations can be conveniently performed since the space inside the nacelle cover is enough to work.
However, in most small and medium wind turbines, the tower is too small to allow an elevator inside, and the only way to access the nacelle through the tower is by means of a ladder fixed outside of it, although in the bigger designs sometimes the ladder can be placed inside.
Moreover, a second problem once the worker has climbed to the tower top, is that he has not an adequate and safe place to stand while performing the maintenance operations, with good access to the nacelle components.
To solve this problem, many small and medium size wind turbines are equipped with a platform at the top of the tower, just below the yaw gear, which is reached by means of the mentioned ladder (in case of inside ladders, a door is provided at the top of the tower). Standing there, the worker removes the cover to operate on the components, a difficult job due to the small size of the platform (limited by the overhang distance between tower and blades) and, especially in the case of bigger designs, because some of the parts can be hardly reached from the working position. On the other hand, this fixed platform affects negatively to the aesthetics of the turbine and can even induce a shadow effect on the rotor when the turbine is turning, increasing loads.
In other small and medium size wind turbines, lifting platforms or cranes must be used to reach and work on the nacelle components during maintenance, increasing the O&M costs and adding the problem of the limited availability of these devices. Finally, in some turbines the nacelle has to be brought down in order to perform the maintenance operations on the ground, a complex and time-consuming practice, especially in the bigger turbines of this range.
In all cases, the nacelle cover has to be removed to reach the elements of the wind turbine equipment.